Visible-Light-Promoted Diboron-Mediated Transfer Hydrogenation Of Azobenzenes To Hydrazobenzenes

A visible-light-promoted transfer hydrogenation of azobenzenes has been developed. In the presence of B(2)pin(2) and upon visible-light irradiation, the reactions proceeded smoothly in methanol at ambient temperature. The azobenzenes with diverse functional groups have been reduced to the corresponding hydrazobenzenes with a yield of up to 96%. Preliminary mechanistic studies indicated that the hydrogen atom comes from the solvent and the transformation is achieved through a radical pathway.